Feedback control circuit and power supply apparatus using dimming adjustment and forward voltage control

Abstract

There are provided a feedback control circuit and power supply apparatus using dimming adjustment and forward voltage control. The feedback control circuit includes: a voltage detection unit detecting an output voltage from a transformer and providing a detection voltage; a dimming unit generating a varied dimming signal; and a feedback circuit unit comparing the detection voltage with a reference voltage varied according to the dimming signal and providing a feedback voltage for controlling a power transmission ratio of the transformer.

What is claimed is: 
     
         1 . A feedback control circuit comprising:
 a voltage detection unit detecting an output voltage from a transformer and providing a detection voltage;   a dimming unit generating a varied dimming signal; and   a feedback circuit unit comparing the detection voltage with a reference voltage varied according to the dimming signal and providing a feedback voltage for controlling a power transmission ratio of the transformer.   
     
     
         2 . The feedback control circuit of  claim 1 , wherein the voltage detection unit comprises:
 a first detection resistor having one end connected to an output node connected to an output terminal of the transformer and the other end; and   a second detection resistor having one end connected to the other end of the first detection resistor and the other end connected to a ground,   wherein the detection voltage is provided from a detection connection node between the first detection resistor and the second detection resistor.   
     
     
         3 . The feedback control circuit of  claim 1 , wherein the dimming unit includes a variable resistor providing a resistance value varied by the dimming signal. 
     
     
         4 . The feedback control circuit of  claim 3 , wherein the feedback circuit unit comprises:
 a reference voltage generation unit dividing an operating voltage according to a voltage dividing ratio adjusted according to a resistance value from the variable resistor of the dimming unit; and   a comparison unit providing the feedback voltage corresponding to a difference between the detection voltage and the reference voltage.   
     
     
         5 . The feedback control circuit of  claim 4 , wherein the reference voltage generation unit comprises:
 a first dividing resistor having one end connected to an input terminal of the operating voltage and the other end; and   a second dividing resistor having one end connected to the other end of the first dividing resistor and the other end connected to a ground,   wherein the reference voltage is provided from a division connection node between the first dividing resistor and the second dividing resistor and the second dividing resistor is connected to the variable resistor of the dimming unit in parallel, according to which the voltage dividing ratio in the division connection node is varied.   
     
     
         6 . The feedback control circuit of  claim 1 , wherein the dimming unit comprises a pulse generation unit providing a pulse signal having a low level and a high level, as a dimming signal. 
     
     
         7 . The feedback control circuit of  claim 3 , wherein the feedback circuit unit comprises:
 a reference voltage generation unit dividing a pre-set operating voltage to generate a reference voltage, the reference voltage being varied according to the pulse signal; and   a comparison unit providing the feedback voltage corresponding to a difference between the detection voltage and the reference voltage.   
     
     
         8 . The feedback control circuit of  claim 7 , wherein the reference voltage generation unit comprises:
 a first dividing resistor having one end connected to an input terminal of the operating voltage and the other end; and   a second dividing resistor having one end connected to the other end of the first dividing resistor and the other end connected to a ground,   wherein the reference voltage is provided from a division connection node between the first dividing resistor and the second dividing resistor, and an output terminal of the dimming unit is connected to the division connection node, so the reference voltage is varied according to the pulse signal.   
     
     
         9 . A power supply apparatus comprising:
 a transformer transmitting power according to a power transmission ratio between a primary winding and a secondary winding to provide an output voltage for driving an illuminating unit;   a voltage detection unit detecting the output voltage from the transformer and providing a detection voltage;   a dimming unit generating varied dimming signal;   a feedback circuit unit comparing the detection voltage with a reference voltage varied according to the dimming signal and providing a feedback voltage;   a signal transmission unit transmitting the feedback voltage; and   a pulse width modulation (PWM) controller controlling the power transmission ratio between the primary winding and the secondary winding of the transformer based on the feedback voltage transmitted from the signal transmission unit.   
     
     
         10 . The power supply apparatus of  claim 9 , wherein the voltage detection unit comprises:
 a first detection resistor having one end connected to an output node connected to an output terminal of the transformer and the other end; and   a second detection resistor having one end connected to the other end of the first detection resistor and the other end connected to a ground,   wherein the detection voltage is provided from a detection connection node between the first detection resistor and the second detection resistor.   
     
     
         11 . The power supply apparatus of  claim 9 , wherein the dimming unit includes a variable resistor providing a resistance value varied by the dimming signal. 
     
     
         12 . The power supply apparatus of  claim 11 , wherein the feedback circuit unit comprises:
 a reference voltage generation unit dividing an operating voltage according to a voltage dividing ratio adjusted according to a resistance value from the variable resistor of the dimming unit; and   a comparison unit providing the feedback voltage corresponding to a difference between the detection voltage and the reference voltage.   
     
     
         13 . The power supply apparatus of  claim 12 , wherein the reference voltage generation unit comprises:
 a first dividing resistor having one end connected to an input terminal of the operating voltage and the other end; and   a second dividing resistor having one end connected to the other end of the first dividing resistor and the other end connected to a ground,   wherein the reference voltage is provided from a division connection node between the first dividing resistor and the second dividing resistor and the second dividing resistor is connected to the variable resistor of the dimming unit in parallel, according to which the voltage dividing ratio in the division connection node is varied.   
     
     
         14 . The power supply apparatus of  claim 9 , wherein the dimming unit includes a pulse generation unit providing a pulse signal having a low level and a high level, as a dimming signal. 
     
     
         15 . The power supply apparatus of  claim 11 , wherein the feedback circuit unit comprises:
 a reference voltage generation unit dividing a pre-set operating voltage to generate a reference voltage, the reference voltage being varied according to the pulse signal; and   a comparison unit providing the feedback voltage corresponding to a difference between the detection voltage and the reference voltage.   
     
     
         16 . The power supply apparatus of  claim 15 , wherein the reference voltage generation unit comprises:
 a first dividing resistor having one end connected to an input terminal of the operating voltage and the other end; and   a second dividing resistor having one end connected to the other end of the first dividing resistor and the other end connected to a ground,   wherein the reference voltage is provided from a division connection node between the first dividing resistor and the second dividing resistor, and an output terminal of the dimming unit is connected to the division connection node, so the reference voltage is varied according to the pulse signal.